Device-to-device (D2D) communication has been developed to meet growing capacity demands due to rapid growth of wireless data services. In a D2D communication scenario, two user equipment (UEs) devices directly communicate with each other without having the payload traversed through the backhaul network. D2D communication is a promising feature that can potentially scale the capacity of the network, improve network resource utilization, such as network throughput, spectrum utilization, reduce transmission delays and offload traffic from the network nodes, as well as improve coverage for user terminals (UE's) that do not have network coverage.
The performance and advantages of D2D communication is currently an active topic of investigation in 3GPP (3rd Generation Partnership Program) RAN (Radio Access Network) forums, for use in wireless communications technologies such as those governed by 3GPP (LTE (Long Term Evolution) and LTE-Advanced (LTE-A) standards.
D2D communication may be bi-directional, where both user terminals receive and transmit using the same or different resources. D2D communication may also be used in a scenario where one of the user terminals transmits and the other one receives the signals. Still further, D2D communication may be used in a point-to-multipoint scenario, such as for example multicast, or broadcast communications, when a plurality of devices receive signals from the same transmitting device. This scenario is particularly useful for emergency services or public safety operation to spread vital information to several devices in an affected area. Still further, D2D communications may be used also for local social networks, content sharing, advertising, and various mobile-to-mobile applications.
In some wireless systems, the D2D UEs operate under the supervision of a radio access network, referred to as cellular network assisted D2D communications. In this case, UEs in the vicinity of each other can establish a direct radio link, i.e. a D2D direct bearer. This direct radio link is referred to as ‘network (NW) link’ or a ‘D2D-NW link’. The D2D-NW link is used for example for resource assignment for D2D communication, maintenance of radio link quality of D2D communication link, etc. While UEs communicate over the D2D-NW link, they also maintain a cellular connection with their respective serving eNB. Furthermore, in some scenarios, D2D UEs may operate to establish direct communication without the intervention of the network infrastructure.
The specification uses the term ‘network node’ for any kind of network equipment including but not limited to eNodeB's (eNB), Node B's (NB), base stations (BS), wireless access points (AP), base station controllers (BSC), radio network controllers (RNC), relay, donor node controlling relays, base transceiver stations (BTS), transmission points, transmission nodes, remote radio units (RRU), remote radio heads (RRH), nodes in distributed antenna system (DAS), core network nodes, mobility management entities (MME), etc.
The term ‘D2D capable UE’ or ‘D2D wireless UE’ or D2D wireless device’ is used in this specification for any type of wireless device, which is capable of at least D2D communication through a wireless link. In some embodiments, the UE may be a mobile communication device, a subscriber station, or another device that is configured to communicate with a wireless system in conformance with an appropriate protocol. Examples of such D2D wireless devices could be sensors, modems, smart phones, machine type (MTC) devices, PDAs, iPADs, tablets, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, etc.
The D2D devices that communicate with each-other are called in some instance a ‘D2D pair’, and the communication between the D2D wireless devices of the pair is referred to as ‘D2D communication’, which takes place along a ‘D2D link’.
The specification also uses the term ‘wireless access network (WAN) UE’, or ‘WAN device’ to a device that is capable to UL and DL communication with a network node. Example of these devices are, as for the D2D devices, smart phones, MCT devices, PDAs, iPADs, tablets, LEE, LME, USB dongles, sensors, modems, etc. The term ‘candidate WAN UE’ or ‘candidate WAN device’ is used for a WAN device that is considered by the network node as a candidate to share the transmission resources with a D2D pair. The communication between the WAN devices and the network node is referred to as ‘WAN communication’ which takes place along a ‘WAN link’.
Although terminology from 3GPP LTE (or E-UTRAN) is used herein, this should not be seen as limiting the embodiments described here to LTE systems only. Other wireless systems, including WCDMA, UTRA FDD, UTRA TDD, and GSM/GERAN/EDGE and other current and future technologies, may also benefit from exploiting the ideas covered within this disclosure. Furthermore, this description may apply to scenarios in which network nodes employ differing radio access technologies (RATs). In some embodiments, short-range technologies, such as Bluetooth or Wi-Fi may be used. In other embodiments, D2D operation may reuse licensed LTE spectrum or unlicensed LTE spectrum. D2D communication may be non-transparent to the wireless system and may occur on a cellular spectrum (i.e. in-band), or unlicensed spectrum (i.e. out-band).
The embodiments described refer to D2D wireless devices are applicable to single carrier or multi-carrier or carrier aggregation based D2D communication.
As well, in the context of this specification, the term ‘downlink’ (DL) is used for the transmission from a network node to a user device, and the term ‘uplink’ (UL) is used for the transmission from a user device to a network node.